Patent GB-337829-A (GB)
Title: Improvements in or relating to automatic switches for use in telephone or like systems
IPC: H04Q3/00
Filed: 1929-08-09
Abstract: 337,829. Automatic Telephone Manufacturing Co., Ltd., and Flenley, A. E. Aug. 9, 1929. Automatic exchange systems; party line systems.-In a connector used for both individual and party lines, a relay operated over a fourth wiper in a party-line call disconnects normal ring- ing current and prepares a circuit whereby a minor switch is set by an additional digit to determine the ringing code, the code ringing circuit being finally completed by a relay which acts also as a busy relay. Calls to individual lines. Line and release relays A, B pull up and the start lead 13 for ringing and tone generators is grounded. The first digit is repeated to relay C and magnet V in series and C relapses to complete a circuit for relay E and magnet R. Relay E opens the circuit of party-line discriminating relay PL, connects relay G to the test wiper P, and closes an alternative circuit for itself and R in case G operates when P passes busy contacts. If the line is busy, G pulls up, opens a further point in the circuit of PL, connects up wipers of ringing digit switch MS without effect in the present case, connects up busy tone lead 15, and locks up when E has fallen back. If the line is free G remains inert, and, on the relapse of E, switching relay H pulls up and locks, connects up ringing tell-tale condenser RB, and completes the ring- ing circuit 17, 18 which includes contacts of PL. The connection is completed in normal manner. Party line call. Relay H operates as above if the line is idle, but PL operates over wiper P1 to ground on party line terminals, opens the normal ringing circuit and connects the impulse circuit to magnet MR of the ringing digit switch MS. Provision is made for up to ten parties on a line, the bells being connected between one or other of the speaking wires and ground, and five different code sets being available over MS and common to a group of connectors. Assuming this digit to be 1, the switch MS connects up the code ringing set shown in Fig. 2. When E relapses at the end of the third digit, G (lower) operates in series with AA, Fig. 2, locks over its upper winding, opens the circuit of MR, releases PL, and connects up the code ringing circuit over wipers PR2, PR1. Relay AA connects a ground pulse from 25 to magnet DM of code ringing switch CR which steps off normal so that AA relapses but AB pulls up to connect further ground pulses (slow) to DM. When CR reaches contacts 7, AC pulls up, locks and connects AE to the pulse lead thereby connecting continuous ringing lead 26 over PR2 to positive wire. This ringing circuit is also completed during the next two ground pulses, but when CR arrives at contacts 10, AD pulls up and disconnects AE, with the result that a silent period ensues until CR reaches contacts 11 when AD relapses and permits AE to operate during the next two ground pulses. When CR arrives at contacts 13, AB falls back, releases AC, and disconnects the pulse lead, but if the wanted party has not replied, AA again operates and the above sequence of events is repeated until he replies since the wiring of the two halves of CR is identical. When F pulls up on reply of the wanted party, the circuit of G (lower) is opened so that ringing is tripped and the code ringing switch ceases to operate on completion of the cycle. If the reply occurs in a silent period, F is operated by direct ground at ael. If another final selector selects the same code switch OR, multilation of the code does not occur since relay G in that selector cannot operate until CR reaches the commencement of a cycle. Reverting calls. The switch shown is unsuitable for this purpose, and such calls may be effected by special switches reached over a particular level of a preceding switch in response to a revertive call number. The special switch is then set by the last two digits to send appropriate ringing current to the calling and called parties. If however the switch' shown is used in an office. of less than 100 lines, reverting calls may be completed by an operator reached by dialling 0, the dotted line connections being provided. Tenth level springs NPS1, NPS2 respectively ground lead 40 to signal the operator, and connect ringing tone to inform the calling party that operator is being signalled. When the operator plugs into the line, a relay in the sleeve circuit releases the final selector and busies the line. The operator asks the calling party to replace his receiver and rings the desired party. Talking battery is fed from the cord circuit.